Fix: utils.c: check str*dup OOM

[lttng-tools.git] / src / common / utils.c

/*
 * Copyright (C) 2012 - David Goulet <dgoulet@efficios.com>
 * Copyright (C) 2013 - Raphaël Beamonte <raphael.beamonte@gmail.com>
 * Copyright (C) 2013 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License, version 2 only, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _GNU_SOURCE
#include <assert.h>
#include <ctype.h>
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <inttypes.h>
#include <grp.h>
#include <pwd.h>
#include <sys/file.h>

#include <common/common.h>
#include <common/runas.h>

#include "utils.h"
#include "defaults.h"

/*
 * Return a partial realpath(3) of the path even if the full path does not
 * exist. For instance, with /tmp/test1/test2/test3, if test2/ does not exist
 * but the /tmp/test1 does, the real path for /tmp/test1 is concatened with
 * /test2/test3 then returned. In normal time, realpath(3) fails if the end
 * point directory does not exist.
 * In case resolved_path is NULL, the string returned was allocated in the
 * function and thus need to be freed by the caller. The size argument allows
 * to specify the size of the resolved_path argument if given, or the size to
 * allocate.
 */
LTTNG_HIDDEN
char *utils_partial_realpath(const char *path, char *resolved_path, size_t size)
{
	char *cut_path, *try_path = NULL, *try_path_prev = NULL;
	const char *next, *prev, *end;

	/* Safety net */
	if (path == NULL) {
		goto error;
	}

	/*
	 * Identify the end of the path, we don't want to treat the
	 * last char if it is a '/', we will just keep it on the side
	 * to be added at the end, and return a value coherent with
	 * the path given as argument
	 */
	end = path + strlen(path);
	if (*(end-1) == '/') {
		end--;
	}

	/* Initiate the values of the pointers before looping */
	next = path;
	prev = next;
	/* Only to ensure try_path is not NULL to enter the while */
	try_path = (char *)next;

	/* Resolve the canonical path of the first part of the path */
	while (try_path != NULL && next != end) {
		/*
		 * If there is not any '/' left, we want to try with
		 * the full path
		 */
		next = strpbrk(next + 1, "/");
		if (next == NULL) {
			next = end;
		}

		/* Cut the part we will be trying to resolve */
		cut_path = strndup(path, next - path);
		if (cut_path == NULL) {
			PERROR("strndup");
			goto error;
		}

		/* Try to resolve this part */
		try_path = realpath((char *)cut_path, NULL);
		if (try_path == NULL) {
			/*
			 * There was an error, we just want to be assured it
			 * is linked to an unexistent directory, if it's another
			 * reason, we spawn an error
			 */
			switch (errno) {
			case ENOENT:
				/* Ignore the error */
				break;
			default:
				PERROR("realpath (partial_realpath)");
				goto error;
				break;
			}
		} else {
			/* Save the place we are before trying the next step */
			free(try_path_prev);
			try_path_prev = try_path;
			prev = next;
		}

		/* Free the allocated memory */
		free(cut_path);
	};

	/* Allocate memory for the resolved path if necessary */
	if (resolved_path == NULL) {
		resolved_path = zmalloc(size);
		if (resolved_path == NULL) {
			PERROR("zmalloc resolved path");
			goto error;
		}
	}

	/*
	 * If we were able to solve at least partially the path, we can concatenate
	 * what worked and what didn't work
	 */
	if (try_path_prev != NULL) {
		/* If we risk to concatenate two '/', we remove one of them */
		if (try_path_prev[strlen(try_path_prev) - 1] == '/' && prev[0] == '/') {
			try_path_prev[strlen(try_path_prev) - 1] = '\0';
		}

		/*
		 * Duplicate the memory used by prev in case resolved_path and
		 * path are pointers for the same memory space
		 */
		cut_path = strdup(prev);
		if (cut_path == NULL) {
			PERROR("strdup");
			goto error;
		}

		/* Concatenate the strings */
		snprintf(resolved_path, size, "%s%s", try_path_prev, cut_path);

		/* Free the allocated memory */
		free(cut_path);
		free(try_path_prev);
	/*
	 * Else, we just copy the path in our resolved_path to
	 * return it as is
	 */
	} else {
		strncpy(resolved_path, path, size);
	}

	/* Then we return the 'partially' resolved path */
	return resolved_path;

error:
	free(resolved_path);
	return NULL;
}

/*
 * Make a full resolution of the given path even if it doesn't exist.
 * This function uses the utils_partial_realpath function to resolve
 * symlinks and relatives paths at the start of the string, and
 * implements functionnalities to resolve the './' and '../' strings
 * in the middle of a path. This function is only necessary because
 * realpath(3) does not accept to resolve unexistent paths.
 * The returned string was allocated in the function, it is thus of
 * the responsibility of the caller to free this memory.
 */
LTTNG_HIDDEN
char *utils_expand_path(const char *path)
{
	char *next, *previous, *slash, *start_path, *absolute_path = NULL;
	char *last_token;
	int is_dot, is_dotdot;

	/* Safety net */
	if (path == NULL) {
		goto error;
	}

	/* Allocate memory for the absolute_path */
	absolute_path = zmalloc(PATH_MAX);
	if (absolute_path == NULL) {
		PERROR("zmalloc expand path");
		goto error;
	}

	/*
	 * If the path is not already absolute nor explicitly relative,
	 * consider we're in the current directory
	 */
	if (*path != '/' && strncmp(path, "./", 2) != 0 &&
			strncmp(path, "../", 3) != 0) {
		snprintf(absolute_path, PATH_MAX, "./%s", path);
	/* Else, we just copy the path */
	} else {
		strncpy(absolute_path, path, PATH_MAX);
	}

	/* Resolve partially our path */
	absolute_path = utils_partial_realpath(absolute_path,
			absolute_path, PATH_MAX);

	/* As long as we find '/./' in the working_path string */
	while ((next = strstr(absolute_path, "/./"))) {

		/* We prepare the start_path not containing it */
		start_path = strndup(absolute_path, next - absolute_path);
		if (!start_path) {
			PERROR("strndup");
			goto error;
		}
		/* And we concatenate it with the part after this string */
		snprintf(absolute_path, PATH_MAX, "%s%s", start_path, next + 2);

		free(start_path);
	}

	/* As long as we find '/../' in the working_path string */
	while ((next = strstr(absolute_path, "/../"))) {
		/* We find the last level of directory */
		previous = absolute_path;
		while ((slash = strpbrk(previous, "/")) && slash != next) {
			previous = slash + 1;
		}

		/* Then we prepare the start_path not containing it */
		start_path = strndup(absolute_path, previous - absolute_path);
		if (!start_path) {
			PERROR("strndup");
			goto error;
		}

		/* And we concatenate it with the part after the '/../' */
		snprintf(absolute_path, PATH_MAX, "%s%s", start_path, next + 4);

		/* We can free the memory used for the start path*/
		free(start_path);

		/* Then we verify for symlinks using partial_realpath */
		absolute_path = utils_partial_realpath(absolute_path,
				absolute_path, PATH_MAX);
	}

	/* Identify the last token */
	last_token = strrchr(absolute_path, '/');

	/* Verify that this token is not a relative path */
	is_dotdot = (strcmp(last_token, "/..") == 0);
	is_dot = (strcmp(last_token, "/.") == 0);

	/* If it is, take action */
	if (is_dot || is_dotdot) {
		/* For both, remove this token */
		*last_token = '\0';

		/* If it was a reference to parent directory, go back one more time */
		if (is_dotdot) {
			last_token = strrchr(absolute_path, '/');

			/* If there was only one level left, we keep the first '/' */
			if (last_token == absolute_path) {
				last_token++;
			}

			*last_token = '\0';
		}
	}

	return absolute_path;

error:
	free(absolute_path);
	return NULL;
}

/*
 * Create a pipe in dst.
 */
LTTNG_HIDDEN
int utils_create_pipe(int *dst)
{
	int ret;

	if (dst == NULL) {
		return -1;
	}

	ret = pipe(dst);
	if (ret < 0) {
		PERROR("create pipe");
	}

	return ret;
}

/*
 * Create pipe and set CLOEXEC flag to both fd.
 *
 * Make sure the pipe opened by this function are closed at some point. Use
 * utils_close_pipe().
 */
LTTNG_HIDDEN
int utils_create_pipe_cloexec(int *dst)
{
	int ret, i;

	if (dst == NULL) {
		return -1;
	}

	ret = utils_create_pipe(dst);
	if (ret < 0) {
		goto error;
	}

	for (i = 0; i < 2; i++) {
		ret = fcntl(dst[i], F_SETFD, FD_CLOEXEC);
		if (ret < 0) {
			PERROR("fcntl pipe cloexec");
			goto error;
		}
	}

error:
	return ret;
}

/*
 * Create pipe and set fd flags to FD_CLOEXEC and O_NONBLOCK.
 *
 * Make sure the pipe opened by this function are closed at some point. Use
 * utils_close_pipe(). Using pipe() and fcntl rather than pipe2() to
 * support OSes other than Linux 2.6.23+.
 */
LTTNG_HIDDEN
int utils_create_pipe_cloexec_nonblock(int *dst)
{
	int ret, i;

	if (dst == NULL) {
		return -1;
	}

	ret = utils_create_pipe(dst);
	if (ret < 0) {
		goto error;
	}

	for (i = 0; i < 2; i++) {
		ret = fcntl(dst[i], F_SETFD, FD_CLOEXEC);
		if (ret < 0) {
			PERROR("fcntl pipe cloexec");
			goto error;
		}
		/*
		 * Note: we override any flag that could have been
		 * previously set on the fd.
		 */
		ret = fcntl(dst[i], F_SETFL, O_NONBLOCK);
		if (ret < 0) {
			PERROR("fcntl pipe nonblock");
			goto error;
		}
	}

error:
	return ret;
}

/*
 * Close both read and write side of the pipe.
 */
LTTNG_HIDDEN
void utils_close_pipe(int *src)
{
	int i, ret;

	if (src == NULL) {
		return;
	}

	for (i = 0; i < 2; i++) {
		/* Safety check */
		if (src[i] < 0) {
			continue;
		}

		ret = close(src[i]);
		if (ret) {
			PERROR("close pipe");
		}
	}
}

/*
 * Create a new string using two strings range.
 */
LTTNG_HIDDEN
char *utils_strdupdelim(const char *begin, const char *end)
{
	char *str;

	str = zmalloc(end - begin + 1);
	if (str == NULL) {
		PERROR("zmalloc strdupdelim");
		goto error;
	}

	memcpy(str, begin, end - begin);
	str[end - begin] = '\0';

error:
	return str;
}

/*
 * Set CLOEXEC flag to the give file descriptor.
 */
LTTNG_HIDDEN
int utils_set_fd_cloexec(int fd)
{
	int ret;

	if (fd < 0) {
		ret = -EINVAL;
		goto end;
	}

	ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
	if (ret < 0) {
		PERROR("fcntl cloexec");
		ret = -errno;
	}

end:
	return ret;
}

/*
 * Create pid file to the given path and filename.
 */
LTTNG_HIDDEN
int utils_create_pid_file(pid_t pid, const char *filepath)
{
	int ret;
	FILE *fp;

	assert(filepath);

	fp = fopen(filepath, "w");
	if (fp == NULL) {
		PERROR("open pid file %s", filepath);
		ret = -1;
		goto error;
	}

	ret = fprintf(fp, "%d\n", pid);
	if (ret < 0) {
		PERROR("fprintf pid file");
	}

	fclose(fp);
	DBG("Pid %d written in file %s", pid, filepath);
error:
	return ret;
}

/*
 * Create lock file to the given path and filename.
 * Returns the associated file descriptor, -1 on error.
 */
LTTNG_HIDDEN
int utils_create_lock_file(const char *filepath)
{
	int ret;
	int fd;

	assert(filepath);

	fd = open(filepath, O_CREAT,
		O_WRONLY | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
	if (fd < 0) {
		PERROR("open lock file %s", filepath);
		ret = -1;
		goto error;
	}

	/*
	 * Attempt to lock the file. If this fails, there is
	 * already a process using the same lock file running
	 * and we should exit.
	 */
	ret = flock(fd, LOCK_EX | LOCK_NB);
	if (ret) {
		WARN("Could not get lock file %s, another instance is running.",
			filepath);
		close(fd);
		fd = ret;
		goto error;
	}

error:
	return fd;
}

/*
 * Recursively create directory using the given path and mode.
 *
 * On success, return 0 else a negative error code.
 */
LTTNG_HIDDEN
int utils_mkdir_recursive(const char *path, mode_t mode)
{
	char *p, tmp[PATH_MAX];
	size_t len;
	int ret;

	assert(path);

	ret = snprintf(tmp, sizeof(tmp), "%s", path);
	if (ret < 0) {
		PERROR("snprintf mkdir");
		goto error;
	}

	len = ret;
	if (tmp[len - 1] == '/') {
		tmp[len - 1] = 0;
	}

	for (p = tmp + 1; *p; p++) {
		if (*p == '/') {
			*p = 0;
			if (tmp[strlen(tmp) - 1] == '.' &&
					tmp[strlen(tmp) - 2] == '.' &&
					tmp[strlen(tmp) - 3] == '/') {
				ERR("Using '/../' is not permitted in the trace path (%s)",
						tmp);
				ret = -1;
				goto error;
			}
			ret = mkdir(tmp, mode);
			if (ret < 0) {
				if (errno != EEXIST) {
					PERROR("mkdir recursive");
					ret = -errno;
					goto error;
				}
			}
			*p = '/';
		}
	}

	ret = mkdir(tmp, mode);
	if (ret < 0) {
		if (errno != EEXIST) {
			PERROR("mkdir recursive last piece");
			ret = -errno;
		} else {
			ret = 0;
		}
	}

error:
	return ret;
}

/*
 * Create the stream tracefile on disk.
 *
 * Return 0 on success or else a negative value.
 */
LTTNG_HIDDEN
int utils_create_stream_file(const char *path_name, char *file_name, uint64_t size,
		uint64_t count, int uid, int gid, char *suffix)
{
	int ret, out_fd, flags, mode;
	char full_path[PATH_MAX], *path_name_suffix = NULL, *path;
	char *extra = NULL;

	assert(path_name);
	assert(file_name);

	ret = snprintf(full_path, sizeof(full_path), "%s/%s",
			path_name, file_name);
	if (ret < 0) {
		PERROR("snprintf create output file");
		goto error;
	}

	/* Setup extra string if suffix or/and a count is needed. */
	if (size > 0 && suffix) {
		ret = asprintf(&extra, "_%" PRIu64 "%s", count, suffix);
	} else if (size > 0) {
		ret = asprintf(&extra, "_%" PRIu64, count);
	} else if (suffix) {
		ret = asprintf(&extra, "%s", suffix);
	}
	if (ret < 0) {
		PERROR("Allocating extra string to name");
		goto error;
	}

	/*
	 * If we split the trace in multiple files, we have to add the count at the
	 * end of the tracefile name
	 */
	if (extra) {
		ret = asprintf(&path_name_suffix, "%s%s", full_path, extra);
		if (ret < 0) {
			PERROR("Allocating path name with extra string");
			goto error_free_suffix;
		}
		path = path_name_suffix;
	} else {
		path = full_path;
	}

	flags = O_WRONLY | O_CREAT | O_TRUNC;
	/* Open with 660 mode */
	mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;

	if (uid < 0 || gid < 0) {
		out_fd = open(path, flags, mode);
	} else {
		out_fd = run_as_open(path, flags, mode, uid, gid);
	}
	if (out_fd < 0) {
		PERROR("open stream path %s", path);
		goto error_open;
	}
	ret = out_fd;

error_open:
	free(path_name_suffix);
error_free_suffix:
	free(extra);
error:
	return ret;
}

/*
 * Change the output tracefile according to the given size and count The
 * new_count pointer is set during this operation.
 *
 * From the consumer, the stream lock MUST be held before calling this function
 * because we are modifying the stream status.
 *
 * Return 0 on success or else a negative value.
 */
LTTNG_HIDDEN
int utils_rotate_stream_file(char *path_name, char *file_name, uint64_t size,
		uint64_t count, int uid, int gid, int out_fd, uint64_t *new_count,
		int *stream_fd)
{
	int ret;

	assert(new_count);
	assert(stream_fd);

	ret = close(out_fd);
	if (ret < 0) {
		PERROR("Closing tracefile");
		goto error;
	}

	if (count > 0) {
		*new_count = (*new_count + 1) % count;
	} else {
		(*new_count)++;
	}

	ret = utils_create_stream_file(path_name, file_name, size, *new_count,
			uid, gid, 0);
	if (ret < 0) {
		goto error;
	}
	*stream_fd = ret;

	/* Success. */
	ret = 0;

error:
	return ret;
}


/**
 * Parse a string that represents a size in human readable format. It
 * supports decimal integers suffixed by 'k', 'K', 'M' or 'G'.
 *
 * The suffix multiply the integer by:
 * 'k': 1024
 * 'M': 1024^2
 * 'G': 1024^3
 *
 * @param str	The string to parse.
 * @param size	Pointer to a uint64_t that will be filled with the
 *		resulting size.
 *
 * @return 0 on success, -1 on failure.
 */
LTTNG_HIDDEN
int utils_parse_size_suffix(const char * const str, uint64_t * const size)
{
	int ret;
	uint64_t base_size;
	long shift = 0;
	const char *str_end;
	char *num_end;

	if (!str) {
		DBG("utils_parse_size_suffix: received a NULL string.");
		ret = -1;
		goto end;
	}

	/* strtoull will accept a negative number, but we don't want to. */
	if (strchr(str, '-') != NULL) {
		DBG("utils_parse_size_suffix: invalid size string, should not contain '-'.");
		ret = -1;
		goto end;
	}

	/* str_end will point to the \0 */
	str_end = str + strlen(str);
	errno = 0;
	base_size = strtoull(str, &num_end, 0);
	if (errno != 0) {
		PERROR("utils_parse_size_suffix strtoull");
		ret = -1;
		goto end;
	}

	if (num_end == str) {
		/* strtoull parsed nothing, not good. */
		DBG("utils_parse_size_suffix: strtoull had nothing good to parse.");
		ret = -1;
		goto end;
	}

	/* Check if a prefix is present. */
	switch (*num_end) {
	case 'G':
		shift = GIBI_LOG2;
		num_end++;
		break;
	case 'M': /*  */
		shift = MEBI_LOG2;
		num_end++;
		break;
	case 'K':
	case 'k':
		shift = KIBI_LOG2;
		num_end++;
		break;
	case '\0':
		break;
	default:
		DBG("utils_parse_size_suffix: invalid suffix.");
		ret = -1;
		goto end;
	}

	/* Check for garbage after the valid input. */
	if (num_end != str_end) {
		DBG("utils_parse_size_suffix: Garbage after size string.");
		ret = -1;
		goto end;
	}

	*size = base_size << shift;

	/* Check for overflow */
	if ((*size >> shift) != base_size) {
		DBG("utils_parse_size_suffix: oops, overflow detected.");
		ret = -1;
		goto end;
	}

	ret = 0;
end:
	return ret;
}

/*
 * fls: returns the position of the most significant bit.
 * Returns 0 if no bit is set, else returns the position of the most
 * significant bit (from 1 to 32 on 32-bit, from 1 to 64 on 64-bit).
 */
#if defined(__i386) || defined(__x86_64)
static inline unsigned int fls_u32(uint32_t x)
{
	int r;

	asm("bsrl %1,%0\n\t"
		"jnz 1f\n\t"
		"movl $-1,%0\n\t"
		"1:\n\t"
		: "=r" (r) : "rm" (x));
	return r + 1;
}
#define HAS_FLS_U32
#endif

#ifndef HAS_FLS_U32
static __attribute__((unused)) unsigned int fls_u32(uint32_t x)
{
	unsigned int r = 32;

	if (!x) {
		return 0;
	}
	if (!(x & 0xFFFF0000U)) {
		x <<= 16;
		r -= 16;
	}
	if (!(x & 0xFF000000U)) {
		x <<= 8;
		r -= 8;
	}
	if (!(x & 0xF0000000U)) {
		x <<= 4;
		r -= 4;
	}
	if (!(x & 0xC0000000U)) {
		x <<= 2;
		r -= 2;
	}
	if (!(x & 0x80000000U)) {
		x <<= 1;
		r -= 1;
	}
	return r;
}
#endif

/*
 * Return the minimum order for which x <= (1UL << order).
 * Return -1 if x is 0.
 */
LTTNG_HIDDEN
int utils_get_count_order_u32(uint32_t x)
{
	if (!x) {
		return -1;
	}

	return fls_u32(x - 1);
}

/**
 * Obtain the value of LTTNG_HOME environment variable, if exists.
 * Otherwise returns the value of HOME.
 */
LTTNG_HIDDEN
char *utils_get_home_dir(void)
{
	char *val = NULL;
	struct passwd *pwd;

	val = getenv(DEFAULT_LTTNG_HOME_ENV_VAR);
	if (val != NULL) {
		goto end;
	}
	val = getenv(DEFAULT_LTTNG_FALLBACK_HOME_ENV_VAR);
	if (val != NULL) {
		goto end;
	}

	/* Fallback on the password file entry. */
	pwd = getpwuid(getuid());
	if (!pwd) {
		goto end;
	}
	val = pwd->pw_dir;

	DBG3("Home directory is '%s'", val);

end:
	return val;
}

/**
 * Get user's home directory. Dynamically allocated, must be freed
 * by the caller.
 */
LTTNG_HIDDEN
char *utils_get_user_home_dir(uid_t uid)
{
	struct passwd pwd;
	struct passwd *result;
	char *home_dir = NULL;
	char *buf = NULL;
	long buflen;
	int ret;

	buflen = sysconf(_SC_GETPW_R_SIZE_MAX);
	if (buflen == -1) {
		goto end;
	}
retry:
	buf = zmalloc(buflen);
	if (!buf) {
		goto end;
	}

	ret = getpwuid_r(uid, &pwd, buf, buflen, &result);
	if (ret || !result) {
		if (ret == ERANGE) {
			free(buf);
			buflen *= 2;
			goto retry;
		}
		goto end;
	}

	home_dir = strdup(pwd.pw_dir);
end:
	free(buf);
	return home_dir;
}

/*
 * Obtain the value of LTTNG_KMOD_PROBES environment variable, if exists.
 * Otherwise returns an empty string.
 */
LTTNG_HIDDEN
char *utils_get_kmod_probes_list(void)
{
	return getenv(DEFAULT_LTTNG_KMOD_PROBES);
}

/*
 * With the given format, fill dst with the time of len maximum siz.
 *
 * Return amount of bytes set in the buffer or else 0 on error.
 */
LTTNG_HIDDEN
size_t utils_get_current_time_str(const char *format, char *dst, size_t len)
{
	size_t ret;
	time_t rawtime;
	struct tm *timeinfo;

	assert(format);
	assert(dst);

	/* Get date and time for session path */
	time(&rawtime);
	timeinfo = localtime(&rawtime);
	ret = strftime(dst, len, format, timeinfo);
	if (ret == 0) {
		ERR("Unable to strftime with format %s at dst %p of len %zu", format,
				dst, len);
	}

	return ret;
}

/*
 * Return the group ID matching name, else 0 if it cannot be found.
 */
LTTNG_HIDDEN
gid_t utils_get_group_id(const char *name)
{
	struct group *grp;

	grp = getgrnam(name);
	if (!grp) {
		static volatile int warn_once;

		if (!warn_once) {
			WARN("No tracing group detected");
			warn_once = 1;
		}
		return 0;
	}
	return grp->gr_gid;
}

/*
 * Return a newly allocated option string. This string is to be used as the
 * optstring argument of getopt_long(), see GETOPT(3). opt_count is the number
 * of elements in the long_options array. Returns NULL if the string's
 * allocation fails.
 */
LTTNG_HIDDEN
char *utils_generate_optstring(const struct option *long_options,
		size_t opt_count)
{
	int i;
	size_t string_len = opt_count, str_pos = 0;
	char *optstring;

	/*
	 * Compute the necessary string length. One letter per option, two when an
	 * argument is necessary, and a trailing NULL.
	 */
	for (i = 0; i < opt_count; i++) {
		string_len += long_options[i].has_arg ? 1 : 0;
	}

	optstring = zmalloc(string_len);
	if (!optstring) {
		goto end;
	}

	for (i = 0; i < opt_count; i++) {
		if (!long_options[i].name) {
			/* Got to the trailing NULL element */
			break;
		}

		optstring[str_pos++] = (char)long_options[i].val;
		if (long_options[i].has_arg) {
			optstring[str_pos++] = ':';
		}
	}

end:
	return optstring;
}